Stud broken, looking for help/insight.

corporate.joe

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Whelp, I managed to do it... I managed to snap an 8mm post off a GFB cell.

That nut wasn't getting tight and I'm not going gorilla on it but I don't have a torque wrench. I can't give a real estimate but I was using a small 1/4" ratchet, thumb rested on head and tightening with my last two fingers. Anyways I thought it was odd, so I backed the nut completely off the stud and inspected both and the threads looked fine. I guess the bus bar was hiding the failing bit.

So how should I approach a remedy to this situation? I'll provide more pictures in a bit. When something like this happens I like to defuse everything and step away and think.

Thanks
 

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corporate.joe

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Don't confuse the tare of the stud with the welds from the get-go. Last pic shows the worst of the welds before a little smoothing by me.

Looks like a virgin terminal underneath the welded on stud/plate. I do have a drill and tap for 6mm. I have no clue as to how far the terminal can be drilled.
 

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RandR

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Just my observation, remove the cell from the assembly? Do you have something more than hand tools? I think there should be a gap between the bottom of the stud and bus. I have done quite a bit of fastener extraction, but I would be doing it on a mill, not by hand.
 

corporate.joe

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Just my observation, remove the cell from the assembly? Do you have something more than hand tools? I think there should be a gap between the bottom of the stud and bus. I have done quite a bit of fastener extraction, but I would be doing it on a mill, not by hand.
The pack is disassembled.

Hand and battery powered tools. No drill press/mill. Can get access to a drill press.

Since the terminal appears to be bare underneath, I'm thinking about using a drill press to drill and tap it for 6mm by 1mm pitch. I don't see how to remove the remaining welded material, just flatten the peaks so it makes solid contact with the busbar. It's intended to carry the current as it was.

Looking at
for reference, but he started with a pre-drilled depth.

@FilterGuy Any recollection on the depth of your terminal?

I haven't been able to find any datasheets on these particular 277ah GFB cells. @Michael B Caro
 

time2roll

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IIRC people have been drilling similar to about 6mm depth to get 6 threads. Getting the tap to the bottom proves most difficult. Then it is still easy to pull the threads out due to the relatively soft aluminum. I have not done this.
 

Bob B

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Most of the threads for tapping these cells is about repairing one that has stripped threads .... and maybe putting in heli coils.
Most are finishing with a bottoming tap to try to get more threads .... one example on this thread. I think cinergi also made a video.
 

BMcL

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corporate.joe

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I would buy a left-hand drill bit (1/8") and as you drill it out it should spin the broken bolt out.
You must spin the drill in the "loosening" direction as you drill the bolt.
You can use a battery drill. Measure the depth of the other terminal so you know how far down you can drill.

There isn't anything to drill and remove. It's a bare unblemished terminal underneath. I do see where you are going if the situation were different.

It's like they took a bolt with a very short head and welded the head to the top of the terminal.
 

stienman

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Can you find a good welder?

A good welder should be able to make very short pulse welds which will impart very little heat to the cell, similar to how a laser welder works.

Personally, I'd contact your supplier and request their opinion, the internal terminal dimensions in case you do drill, as well as their recommended torque for the remainder of the cells. Buy a torque wrench and make sure you never exceed their limit, and if the terminal breaks off you have reason to suspect manufacturing fault and make a warranty claim.

If you still don't feel comfortable with a regular tig welder, shop around for laser welding companies - you might be surprised at what you can find locally.

Consider drilling and tapping four 4mm holes rather than one 6mm hole. You won't have to go as deep for the same amount of force. Flatten the entire terminal, and go down 5mm, which should be sufficient and safe.

Also, keep in mind that you aren't supporting 500lb with this connection. I'm not sure why people are so keen on ultra-tight connections, but for electrical purposes, as long as you clean both contacts and use an anti-oxidant, you really don't need to press them together with more than a few pounds of force, unless you're running right at the edge of how much surface area you have between the contacts and how much current you need to carry.

If you are concerned about your connections, draw your maximum current from the pack, and measure the voltage between the bus bar and the terminal. As long as it's low, then the connection is fine.
 

rplarry

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I'm a hobby machinist so I know a little about trying to repair this kind of stuff. Its hard to tell from the photos but it looks like there is something sticking up in the center of the hole where the stud pulled off. Is that right? If so then that would have to be removed. Next what is the diameter of the hole? Is it appropriate for a 6mm tap? If not consider drilling a little larger hole and using a 1/4-28 or a 1/4-20 stud to go in there. Once you know the size of the stud you are going to use and have drilled the proper hole you can use a bottoming tap to tap the hole. Usually the depth of the hole should be at least the same as the diameter of the hole maybe a little deeper. 1/4" hole then maybe 5/16" depth.
You are going to do all this drilling with a drill press or better yet a milling machine. Use a fairly high rpm so the drill doesn't grab the soft aluminum and use some good cutting oil. Do all the drilling slowly and you should be fine.
It almost looks like the way they made those things was to start with a battery terminal that was designed to be threaded and before it was threaded they welded the stud on it. If that is the case then the hole is probably already the right size for a 6mm x 1 thread.
Maybe you got lucky in that respect.
Let us know what happens.
 

corporate.joe

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View attachment 66793Corporate Joe - did you manage to get your cell stud fixed? I did the exact same thing tonight.
Sorry I haven't updated this yet. I managed to have a friend with a drill press drill a 5mil hole about 6mil deep. Then I started the tap with an unmodified 6x1mm tap. And then I used another tap that I cut the taper off of the end to ensure I was getting as many threads and as close to the bottom as I could. Used a 20mm black oxide steel set screw for stud. I didn't not remove the leftover weld. That weld had confirmed to my busbar.

I am a little worried about the small air gap between the remainder of the bolt weld and the terminal. I guess if I wanted to remove that it could be done with a mill very carefully.

Joe-
 

Drelovessolar86

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Jul 12, 2021
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Thanks Joe. I’m glad you got it fixed! I’ll be going through this process as well soon. Any reason you didn’t go with an M8 bolt size? Might reduce that gap.
 

MurphyGuy

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I think I would flatten the entire area down.. Machine down the welds and that shiny ring-like area inside the welds until its all one smooth surface.

This is not something you're going to do by hand.. but make a flat surface of the welds, flange, everything.

Then cut a circular shape to fit it.. Drill and tap a series of #6-32 screws all the way around and bolt the new contact plate to it. Once you have a contact plate that can be screwed down with 6 or so small screws, you can do anything you want with it.

Take it to a high school machine shop and they'll probably do it for a small donation, or even free.. Just throw the battery up onto the table of a vertical mill and have someone run an end mill cutter over it until its all flat.
 

corporate.joe

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Thanks Joe. I’m glad you got it fixed! I’ll be going through this process as well soon. Any reason you didn’t go with an M8 bolt size? Might reduce that gap.
I'm on my phone, so not sure how well this will come out. The green represents the gap between the lifted material that the bolt was attached to. The purple is a guess of the actual amount of material that is making contact with the battery terminal.

The m8 would reduce the contact area of lug/busbar to the battery.
I think I would flatten the entire area down.. Machine down the welds and that shiny ring-like area inside the welds until its all one smooth surface.

This is not something you're going to do by hand.. but make a flat surface of the welds, flange, everything.

Then cut a circular shape to fit it.. Drill and tap a series of #6-32 screws all the way around and bolt the new contact plate to it. Once you have a contact plate that can be screwed down with 6 or so small screws, you can do anything you want with it.

Take it to a high school machine shop and they'll probably do it for a small donation, or even free.. Just throw the battery up onto the table of a vertical mill and have someone run an end mill cutter over it until its all flat.

Yeah I'm considering milling it flat in the near future. Highschool machine shop? I've been out of highschool twenty plus years now and we didn't have one of those then. Useful sh*t isn't taught in America anymore.

Joe-
 

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MurphyGuy

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Yeah I'm considering milling it flat in the near future. Highschool machine shop? I've been out of highschool twenty plus years now and we didn't have one of those then. Useful sh*t isn't taught in America anymore.

Joe-
Interesting.. I was in high school back in the 80's and it is where I learned to operate milling machines.. became an electrical engineer, but I can hold my own on any vertical mill or lathe.

Unfortunately, I never bought my own, although I have considered purchasing a South Bend several times over the last few years.

I took an ad out on Craigslist looking for someone with a lathe in their barn.. got a response within three days and the guy did anything I needed for the next 5 years.. cheap too.. $20 here, $15 there... then he moved away so I took another ad out and some other guy contacted me.. Can't really compare prices because the work he did for me was a magnitude more complex and I never gave him any small jobs.

You'd be surprised at how many people have vertical mills in their garages and like to run them just for fun..

But don't try to do it by hand no matter how desperate you get.. it needs to be razor flat..
 

corporate.joe

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Interesting.. I was in high school back in the 80's and it is where I learned to operate milling machines.. became an electrical engineer, but I can hold my own on any vertical mill or lathe.

Unfortunately, I never bought my own, although I have considered purchasing a South Bend several times over the last few years.

I took an ad out on Craigslist looking for someone with a lathe in their barn.. got a response within three days and the guy did anything I needed for the next 5 years.. cheap too.. $20 here, $15 there... then he moved away so I took another ad out and some other guy contacted me.. Can't really compare prices because the work he did for me was a magnitude more complex and I never gave him any small jobs.

You'd be surprised at how many people have vertical mills in their garages and like to run them just for fun..

But don't try to do it by hand no matter how desperate you get.. it needs to be razor flat..
You've got a few years on me. I'm at the very tail end of "generation x."
 
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